Baa!!! – An Idiot’s Guide to Herd Immunity

One of the things I realise is that the anti-vaccination lobby often utilise fairly unorthodox methodology to spread their ideas.

See? Science writing generally tends to stick to fairly well trodden paths. Even pop sci. Popular Science is science written to simplicity and provided with glossy photos and cool diagrams. But the thing with Pop Sci is that it generally sticks to the cool bits of science. It’s easy to sell this cool new rocket than it is to sell the basics.

It is why such magazines rarely advertise a new hygenic toilet despite that fact that is something basic that could save thousands if not millions of lives. It isn’t glamorous.

Neither is this.

Herd Immunity. I write this in response to the Financial Post’s resident quack, Lawrence Solomon.

Normally? I just write about the issue, but this one’s been making the rounds and kind of got me thinking. It would help if new parents to the issue could see the sort of falsehoods spread by “alleged” experts. I also write this under the notion that people will pass this on. So this post will be under a Creative Commons License. You can pass it on, copy paste it and use it as long as you attribute correctly.

So let’s look at what the issue is.

“When vaccination rates are very high, as they still are in the nation as a whole, everyone is protected,” explained USA Today in a recent editorial entitled “Vaccine opt-outs put public health at risk.”

“This ‘herd immunity’ protects the most vulnerable, including those who can’t be vaccinated for medical reasons, infants too young to get vaccinated and people on whom the vaccine doesn’t work. But herd immunity works only when nearly the whole herd joins in. When some refuse vaccinations and seek a free ride, immunity breaks down and everyone is more vulnerable.”

The concept of “herd immunity” first materialized in the 1930s, when Johns Hopkins University’s Arthur Hedrich discovered that, after 55% of Baltimore’s population acquired measles (and thus immunity to measles), the rest of the population, or “herd,” became protected. This concept provides today’s rationale for insisting that everyone be vaccinated.

The thing is? It doesn’t quite explain herd immunity. Let us take a hypothetical disease. It is harmless. Let us say it makes you break out in green spots, has zero percent fatality and 100% transmission. In this case if you are infected and meet another person then the disease will transfer.

When a population is exposed to a disease and everyone in it is vulnerable then the disease cuts through it like wild fire. We forget that diseases spread by vectors and aren’t spontaneous things. With that in mind the disease goes from person to person until the entire population has broken out in green spots. We saw this type of spread in the New World with Measles. Measles effectively  killed a huge number of native Americans. But as a population is exposed to the disease what happens is an equilibrium.

It’s widely seen in predator prey relationships if a predator eats a single species of prey. As the amount of prey increases, the predation rate increases, this causes a drop in the amount of prey which causes a corresponding drop in the amount of predation which in turn causes an increase in prey. In terms of a graph? Prey population goes up and down and so does the predator population. Makes sense right?

The same thing happens with an endemic disease. Eventually you hit a high amount of immunity with most people having had the disease at some point and there is a small but significant population whose immune systems are naive to this “green disease”. As the numbers increase, the incidence of the disease increases which causes a corresponding fall in number of naive people which causes a fall in incidence of disease.

Vaccination basically reduces the incidence of disease.

The idea is that “most” people can be vaccinated. It won’t stop all the disease but what it will do is have a protective effect by disruption of the transmission chain. Imagine if we had a vaccine that makes the spread of our 100% disease abovee to just 10%. That means 1 in  10 people would be immune to it. So with  each transfer there is a 90% chance that the transfer will fail. The disease if defeated by an immune system and it fails to transfer will die out. All you need to do is use basic precautions such as staying at home in self imposed quarantine and “voila” disease doesn’t spread as easily.

That is the how the herd immunity works. Diseases have a latent period and an  infective period and a rebound period. The latent period is the time taken for the disease to become manifest. Most diseases don’t spread at this point. There are a handful that spread. The infective period is when most diseases spread and it is often associated with symptoms. The rebound is when your body returns to normal. Some auto immune or toxins may make you sick during this period of infection too. In proper terminology? There are four stages.

The incubation stage (silent stage– the pathogen has gained entry into the host and starts replicating.) 
The prodromal stage (itchy, runny nose, dry eyes, Clinical Features begin to present) 
The peak (clinical) stage (the disease reaches its highest point of development, severe aches, chills, vomiting, etc.) 
The recovery stage (symptoms have all but completely vanished; pathogen has been mostly eliminated)

The anti-vax would like you to think that you aren’t sick when a disease is incubating and gathering the critical mass of pathogen to begin having an effect. A vaccine works by effectively stopping the disease during the incubation stage. Most diseases are non-infective during this period. As in the traditional methods of mass transfer are not seen. There are no coughs and sneezes to spread germs. There is no vomitting or diarrhoea. The disease is silent. For all you know you are healthy during this period.

The vaccine effectively helps your body skip the middle two stages. Your immune system quickly recognises the pathogen and existing circulating antibodies destroy the small amounts that have  gotten past the non-specific immune system and trigger a large response that effectively  halts the infection before the patient becomes infective.

In November 1966, in announcing a mass vaccination program for measles that would exceed the 55% level reached in Baltimore, the U.S. Public Health Service confidently announced that “Effective use of these vaccines during the coming winter and spring should insure the eradication of measles from the United States in 1967.”

When measles failed to be eradicated, public health experts decided that a 70% or 75% vaccination rate would secure herd immunity. When that proved wrong, the magic number rose to 80%, 83%, 85%, and then it became 90%, according to a 2001 Health Services Research report. Later health experts commonly cited 95%.

Measles CAN be eliminated. It isn’t zoonotic so has no animal reservoir. There are however issues.

Big ones

1. There is a complete lack of will to do so in the developed world

2. People think Measles is harmless. Even if it is, the amount of man hours lost doesn’t figure into people’s calculations

3. It is an airborne disease with relatively low fatality rates and high infection rates. All it needs is one person to not want to play the game.

4. There is a concerted effort to halt all vaccinations as it is profitable among some unscientific, unscrupulous and ignorant quacks

5. There is an associated conspiracy theory and anti-vaccination  is not treated as superstition but being a “savvy customer”.

In short? We were well on our way to making Measles Extinct. If not for the actions of Anti-Vaccine. To this day in India and China the universal vaccination schemes are causing remarkable falls in VPDs (Vaccine Preventable Diseases). Yet in the western  world, the way  anti-vax work is appealing to people’s idea that education is “enough” and utilising a little education to promote a huge piece of ignorance.

In effect the barrier to the spread of the disease has fallen. We made travel  easily. It isn’t enough that everyone in a local place have to be vaccinated but a reservoir of disease can simply export the disease via a carrier on a plane. The current example is the discovery of the polio virus in Brazil due to the World Cup’s fans. When we eliminated Smallpox it was easier because people genuinely feared the disease, knew how much it killed and the anti-vax could simply be quarantined under fear till the virus was eliminated. There were a lot fewer anti-vax then too and a lot more barriers to cheap transit.

But that too was insufficient — measles outbreaks occur even when the vaccinated population exceeds 95%, leading some to say a 98% or 99% vaccination rate is needed to protect the remaining 1% or 2% of the herd. But even that may fall short, since outbreaks occur in fully vaccinated populations.

“The target would be to have 100% of the population vaccinated,” Dr. Gregory Taylor of the Public Health Agency of Canada recently told CBC, voicing an increasingly common perspective among public health professionals. At that point, the balance of the herd that would be protected through mass vaccination would be precisely 0.

John here thinks all outbreaks are equal. At it’s heyday Measles in the USA would be infecting around a million people. The report rate was 50% (since most kids were treated at home) and 500,000 odd people made it to hospitals.

Let us take 500,000 and ignore the home treated. The current outbreak this year? Between January to  May 23rd there have been 288 cases of Measles in the USA. If we extrapolated that for the year? Around 600 people. Less than 1% of the old incidence. That is a “modern” outbreak.

And interestingly enough? The CDC mentions the break down of vaccination status. 280 cases to 8. 280 of them were in  unvaccinated people, 8 in the vaccinated. Mr. Solomon here thinks 8 is an outbreak while ignoring the major cause of the outbreak.

His nonsense. New parents may wonder why I am so rude and condescending. The thing is? If we spoke to NASA and  then turned to Solomon away from the actual Rocket Scientists and asked for his opinion on space research, people would think it was a bit weird. If he then responded “I think space  travel is impossible because we cannot pass through the blanket on which the stars are painted”, you would consider this to be a frightful waste of time.

Yet here  we are. I have to explain something widely considered to be science while people give platforms to the man who has no idea about  the basics of immunology and disease yet considers himself an expert.

The fact is? The USA does not have a 100% vaccination rate. The rising anti-vaccination sentiment means that low vaccination rates are the norm. In many parts of the USA there are rates as low is 65% of roughly  1 in 3 people aren’t vaccinated. By contrast? In many parts of India there are 95% vaccination rates. It may not cover all the vaccines that the USA has but a lot of these are for basic childhood killers and people are willing to vaccinate. The antivax claim it is because these people are uneducated.  That much may be true. They may notice the lack of education and consider doctors to be highly educated and so follow our advice. Or it may genuinely be because doctors are trusted because vaccinations show visible effects and people in India still remember the diseases that can be prevented.

By contrast, the anti-vax routinely pride themselves in education. In fact one of the major claims is the amount of time spent doing research. Look, a discovery isn’t less of one if someone  finds it 10 minutes in by accident. 300,000 man hours of research to make an incorrect claim of discovery doesn’t make it right. And in many cases look at the numbers provided. It’s usually “hundreds of hours”.

The average medical student works around 40 hours a week learning his trade. A month is around 160 hours. A 38 week course is 1440 hours per year. 5 years of that.

And you still aren’t considered an expert in your field unlike the claims of many people who wish to pretend to be medically competent. And this isn’t research. This is just learning.

But even vaccinating 100% of the population wouldn’t be enough, say scientists at the Mayo Clinic’s Vaccine Research Group, because the measles vaccine is a dud with some people, offering no protection at all, and its effectiveness wanes with others, even if they get boosters. According to Tetyana Obukhanych of Stanford University’s School of Medicine, the measles vaccine works as planned with only 25% of the population, leaving the majority of adults who have been vaccinated as children with little or no protection. Up to half of today’s cases involve adults.

Yes. And most of those adults grew up in the 1990s when the vaccination causes autism fear began. Half the cases may involve adults but they are YOUNG adults.

95% of all cases this year until May 2014 (AKA not this month in the USA) involve anti-vax or partially vaccinated people. Unless Solomon here claims that the CDC are simply lying. A common claim among anti-vaccination lobbyists.

It doesn’t matter that these people  are adults, but what their actual vaccination status is.

Oh and that 280 vs 8 thing is worse than it sounds. More than 70% of people are still vaccinated. Let us conservatively claim 80%. Out of 80% only 8 people got the disease. Out of 20% 280 got the disease. When discussing disease incidences the “out of number” (or denominator is important).

Imagine if your kid came back from school and on the report card it says 100 on it. You would be proud of him! What if the maximum score was 1000. That’s an entirely different performance. That 100 means something different when out of 1000. It is why we compare incidence rates. The denominator for anti-vax is much much lower than that of the vaccinated. So despite 95% of all cases being anti-vax the burden of disease is even higher due to their small population.

So let’s take a population  of 80 vaccinated, 20 unvaccinated. 1 Vaccinated catches Measles. The incidence is 1 in 80. if 1 unvaccinated catches the disease then it is 1 in 20. Now imagine if 10 of them catch the disease? That is a 50% infection rate in the unvaccinated.

So those numbers from the CDC are worse for the anti-vaccination than first appears.

Oh and Tetyana shills for quacks. The earliest universal vaccination schemes were in  places like Moscow. Communists love Social Medicine since it is minor changes for major benefit. The Measles incidence rate plummeted. After the first year it dropped by 67% and then to 93%. In 3 years measles rates went from the tens of thousands in the city to dozens.  That 25% rate? Just seems highly  made up.

Unlike childhood measles, adult measles is dangerous: 25% of cases require hospitalization. Measles is especially dangerous when contracted by expectant mothers — studies of hospital outcomes in Los Angeles and Houston found that most suffered serious complications, some died, and their babies often died in the womb.

The issue is moot if the disease is extinct.

Solomon here is trying to imply that even vaccinated women are at risk for Measles because the herd immunity doesn’t work. While Measles can have terrible repercussions for pregnant women through miscarriage and premature labour it is rare.

The dangers extend to infants who, as USA Today points out, are too young to be vaccinated. These entirely helpless members of “the herd” depend on antibodies inherited from their mothers. Yet previously vaccinated mothers have few antibodies to pass on, depriving their babies of protection. The only tried-and-true way for mothers to safeguard their infants — those most at risk of death from measles — remains nature’s way: by ensuring that the mother had previously contracted natural measles.

Again the argument hinges on pathogens behaving in an entirely different way. Solomon would have a Nobel Prize if he could prove that pathogens simply existed without any transmission chain. Solomon’s model simply requires pathogens to spread by magic rather than through known pathways. Solomon’s argument is simple.

Herd Immunity Doesn’t Work because Measles isn’t Eliminated. Never mind the anti-vaccination drive that’s caused a drop in vaccination rates. More mothers are getting measles. Therefore if we eliminate all vaccination then everyone would have Measles earlier and therefore no one would get maternal Measles. And babies wouldn’t get Measles because “mother’s milk”.

The thing is? Babies don’t stop getting Measles at 9 months. The point where most of them are weaned off breast milk and lose the protection. And the point where we vaccinate for measles. A 10 month old baby with measles is still pretty weak and it is a pretty serious infection.

The fact is that mothers who have had Measles tend to live in places where Measles is endemic and so have high antibody titres as their body keeps getting exposed to the virus. There is a simple solution to this. A booster dose given at the age of 20 and 30 for women. Rather than the alternative of 500,000 more sick children a year in the USA.

The yearly burden of Measles is nearly 20 million cases. And this is considered too much even without the fatalities.

In fact, herd immunity — so elusive today — fully existed prior to the vaccine’s introduction. Virtually 100% of the population then contracted measles, typically as children, giving everyone lifelong immunity — and future mothers the means to protect their offspring. In mass vaccinating us, scientists of the 1960s didn’t realize that infecting us with the measles vaccine — a weak version of the natural measles virus — would give us a weak version of the defenses our bodies develop to the real thing.


The infection of measles never gave life long immunity on its own. The society where measles was endemic meant you would get reinfected by measles at various points of your life. Remember those stages of infection? Circulating antibodies would simply destroy the disease before it got to stage where you felt it’s effects.

Back then there were always a naive population created every year that could be affected by outbreaks of the disease. The reason it doesn’t work is that vaccinations schemes tend to be universal and so create sudden immunity across the board effectively denying targets for the pathogen causing it to die out. So there  isn’t any Measles being bandied around to top up your antibody titres.

This is a fantasy. Measles has a fairly high rate of hospitalisation for such a harmless disease. It’s side effects can kill through diarrhoea and pneumonia. Solomon simply ignores the dangerous complications of Measles to portray the rare complications of Measles as common.

Ironically, the Public Health Service considered measles generally benign in the pre-vaccine era. “Complications are infrequent and, with adequate medical care, fatality is rare…. Immunity following recovery is solid and lifelong in duration,” its chief of epidemiology, Alexander Langmuir, acknowledged in “Epidemiologic basis for eradication of measles in 1967.”

Indeed. Back then only 1 in 1000 children would die from Measles.

Broken bones aren’t fatal either but you still pad children’s play areas with soft stuff rather than concrete. And see Measles is deadly if you are poor and malnourished. Most of us in the west are rich enough to “make it”. BUT it will show it’s biggest burden on poor working class families. It’s simple.

Someone has to take time off. Mummy usually. There are no paid days off on low paid jobs. Mostly you just don’t get paid while you stay at home. Tally that up. And malnourishment is seen in the USA too. Those kids will die more than the rich kids that Solomon’s thinking about when he pushes this.

And that’s not a deadly disease. Measles is a child hood disease with a fatality rate if you are in places like rural Africa.

What you should fear are diseases such as Bacterial Meningitis, Pertussis, Rubella, Diptheria  and Pneumonia. Real killers. Funny how when discussing anti-vaccine ideas, no one really brings up rabies vaccine. See in dogs, the vaccine’s helped eliminate rabies as a domestic disease in the USA and the UK. A few deaths happen every year in the USA due to wild animals and in the UK the last deaths were due to travellers.

To India. Where there is no Rabies Vaccination program for pets and huge quantities of stray dogs. It is quite simple. How come the herd immunity works in dogs in the USA but not in humans?

Why, then, did he decide to eradicate this generally harmless and beneficial disease? “To those who ask me, ‘Why do you wish to eradicate measles,’ I reply with the same answer that Hilary used when asked why he wished to climb Mt. Everest. He said, ‘Because it is there.’ To this may be added, ‘…and it can be done.’”

Prior to the vaccination. Measles was responsible for killing around

  • Measles is one of the leading causes of death among young children even though a safe and cost-effective vaccine is available.
  • In 2012, there were 122 000 measles deaths globally – about 330 deaths every day or 14 deaths every hour. 14 preventable deaths from a “harmless and beneficial disease”. An acceptable cost to Mr. Solomon
  • Measles vaccination resulted in a 78% drop in measles deaths between 2000 and 2012 worldwide.
  • In 2012, about 84% of the world’s children received one dose of measles vaccine by their first birthday through routine health services – up from 72% in 2000.
  • Since 2000, more than 1 billion children in high risk countries were vaccinated against the disease through mass vaccination campaigns ― about 145 million of them in 2012.

Just not in the USA. Because of people like Solomon. Who think that the disease was harmless. Consider HIV kills a million people a year and is considered deadly. Measles in it’s day killed 2.5 million people a year. It wiped out civlisations. The “plague” that affected the New World was thought to be Measles. Places like the Pacific Islands were often decimated thanks to it.

Is it ignorance? Is it a blindness to the reality of Measles? Is it a calculated statement for profit?

But yes, Solomon thinks that the 2.6 million deaths a year (1980) was an acceptable number of dead people. Historically speaking?

Outside of Smallpox and Malaria, the big yearly pathogen by death toll was Measles.

Herd immunity sounds fine in theory. But as Stanford’s Dr. Obukhanych concluded, “As with any garbage in-garbage out type of theory, the expectations of the herd-immunity theory are bound to fail in the real world.”

Rather amusing because in the real world Measles is a terrible disease. Dr. Obukhanych misrepresents immunology in order to take a whack at the herd immunity and is a darling of the anti-vax movement because of her claim which we can categorically and repeatedly disprove.


  1. efogoto says

    “Imagine if we had a vaccine that makes the spread of our 100% disease abovee to just 10%. That means 1 in 10 people would be immune to it. So with each transfer there is a 90% chance that the transfer will fail.”

    The middle sentence seems backward to me. If the vaccine changes communicability from 100% to 10%, aren’t 9 in 10 people immune to it?

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